1. Field of the Invention
This invention relates to improvements in wobble run-out compensation for any rotating body having a wobble run-out characteristic relative to a true relationship with its axis of rotation, and more particularly to a two-step compensation method using electronic assistance.
2. Description of the Prior Art
An example of a rotating body that may have a wobble run-out characteristic relative to its axis of rotation is a vehicle wheel. The plane of the wheel rim may not be perpendicular to the axle about which it rotates. In order to compensate for the lack of perpendicularity when mounting instrumentation apparatus on the wheel rim, heretofore mechanical compensation means has been provided to achieve perpendicularity. Mechanical compensation means involves providing adjustable threaded devices between the mounting plate for the instrumentation and a companion plate that is attached to the wheel rim. By adjusting the threaded devices the instrument mounting plate can be brought to a position where it does not wobble and is perpendicular with the axis of rotation of the wheel.
Adjustments with such mechanical means are made using estimates of wobble run-out compensation and often required an iterative process with one adjustment affecting one or more previous adjustments. Previous systems may have included visual aids in compensation adjustments such as toe-light beams, bubble levels, or camber gauges. No previous mechanical compensation system, however, electronically computed and displayed the magnitude and direction of the required manual adjustment.
When the mechanical compensation is completed, the instrument will be true with the axis of rotation and the instrumentation can accurately measure the angular orientation of the wheel axis in both vertical and horizontal planes. The vehicle wheel camber angle is relative to the vertical plane and the vehicle wheel toe angle is related to the horizontal plane of rotation. These two angular wheel positions are well known in the art of vehicle wheel alignment for proper running conditions.
Various electronic compensation systems have been used in the past. For example, U.S. Pat. No. 3,892,042 to Senften discloses an electronic run-out compensation system for electronically compensating for wobble run-out in a rotating body. In Senften the compensation is wholly electronic. As stated in col. 1, lines 54-58, the invention of Senften electronically compensates for wobble run-out characteristics so that no mechanical adjustments are needed. The Senften system works by averaging the wobble run-out from an electronic sensor at any two points 180 degrees apart to give the true plane of the wheel relative to its axis or spindle (see col. 2, lines 4-18).
As noted in Senften, it is known that the wobble follows a sinusoidal curve as the wheel is rotated about its axis or spindle At any two points of the sine wave 180 degrees apart, the deviation from the true plane is equal and opposite. Thus, by choosing any two points 180 degrees apart and electronically adding the values and dividing by two, the value of the angle of the true plane of the wheel axis or spindle is obtained. The angle of the wheel axis can also be determined from three or more measurement points that are separated by any known spacings by averaging the orthogonal component vectors of the measurements.
U.S. Pat. No. 4,138,825 to Pelta shows a purely electronic run-out compensation system (see col. 1, lines 55-61). In pelta, instead of taking two measurements in each of the vertical and horizontal planes to compensate for wobble run-out in both those planes, the electronic system in Pelta uses three measurements and computes the compensation in both planes from those three measurements (see col. 2, lines 16-30).
In like manner, U.S. Pat. No. 4,192,074 to Chang describes an on-the-fly run-out correction system which uses purely electronic compensation for wobble run-out. The operation of the Chang system is described in col. 2, lines 45-68 and col. 3, lines 1-68. In the Chang system the total wobble run-out errors are measured through at least one complete revolution of the vehicle wheel. The wheel is then stopped and the system computes the correction in both planes for the position where the wheel stopped. The wheel is lowered to the ground and the actual or true camber and toe angles of the wheel (corrected for wobble run-out by the system) are displayed for use by the person making the desired adjustments to the wheel.
U.S. Pat. No. 4,274,738 to Hollandsworth et al. also shows an electronic run-out compensation system which displays to the user the amount of wobble run-out compensation to be applied. A summary of the operation of the Hollandsworth et al system is set forth in col. 7, lines 14-68 and col. 8, lines 1-9.